Adjustable spanners and wrenches are particularly useful as they can accommodate nuts and bolts of various size. One common type of adjustable spanner comprises a fixed jaw and a moveable jaw which is journalled to a worm gear that can be rotated by the thumb of a user. Rotation of the worm gear causes the moveable jaw to move relative to the fixed jaw to facilitate gripping of a nut or bolt. One difficulty with this type of adjustable spanner is that adjusting the spanner to engage a nut or bolt can be time consuming particularly in a confined environment and/or where the nut or bolt cannot be easily seen. A further difficulty is that the worm gear is designed to provide a degree of play between the jaws. This may at times result in the spanner slipping when torque is applied. Additionally, in areas where the spanner cannot be rotated a full 360°, applying torque to a nut or bolt requires repeated engagement and disengagement of the spanner with the nut/bolt.
The present inventor has developed numerous alternative adjustable spanners including that described in U.S. Pat. No. 5,568,752. The spanner described in the above referenced U.S. patent comprises a handle provided with a fixed jaw, and a lever pivotally coupled to the handle and to a second jaw. A link is pivotally connected at one end to the second jaw and pivotally connected at an opposite end to the lever. The link carries a cam that rides in an elongate slot cut in a head of the handle, the slot being provided along one surface with a rack of teeth. The cam and slot cooperate to form a locking mechanism which has a first state in which the cam is disengaged from the teeth and wherein the jaws are able to move relative to each other, and a locking state in which the cam is rotated via the link into engagement with the teeth to lock the jaws against movement away from each other.